The estrogen receptors of human mammary tumors and the glucocorticoid receptors of transplantable murine mammary tumors will be analyzed by physical chemical techniques including systematic electrophoresis in highly cross-linked polyacrylamide gels and preparative ion exchange filtration on DEAE-cellulose. One goal of our research is to discriminate among the intracellular receptors for different steroids, the multiple forms of individual receptors, and the serum steroid-binding proteins that may be present in a single target organ. Another goal is to determine whether steroid agonists and antagonists of a given function bind to distinct conformational states of a receptor. The proteins in target organ extracts will be covalently labeled remote from the steroid-binding site with a radioactive isotope other than tritium to assess the purification of the 3H-steroid-receptor complexes. Purification of the receptor subcomponents should contribute to our understanding of the function of the intact complex. BIBLIOGRAPHIC REFERENCES: Sherman, M.R. and Diaz, S.C., In Conference on Biochemical Actions of Progesterone and Progestins, New York, May 5-7, 1976. Ann. N.Y. Acad. Sci. Sherman, M.R. and Miller, L.K., In Abstracts of the Biochemical Society Meeting, San Francisco, June 6-10, 1976, Federation Proc. 35, 1560.